The use of turbochargers to increase the horsepower and torque of an internal combustion engine is well known in the art. With the addition of an exhaust-driven turbocharger, a relatively small, fuel-efficient engine can be used in a vehicle to provide economical operation during normal driving while providing additional horsepower and torque during acceleration and/or full-throttle operation.
A turbocharger includes a compressor and a turbine. The turbine drives the compressor with exhaust energy created by the internal combustion engine. The engine exhaust drives a turbine wheel in the turbine of the turbocharger and is discharged through an exhaust system. The turbine wheel drives a shaft connected to a compressor wheel in the compressor which pressurizes intake air, previously at atmospheric pressure, and forces it typically through an intercooler and over a throttle valve and into an engine intake manifold. Controlling the output of the turbocharger to obtain desired engine operation has been a long-standing problem. Too much output can create erratic engine performance and permanently damage engine components. Too little output causes engine hesitation, loss of power, and inefficient operation. Additionally, changes in atmospheric pressure, ambient temperature, and engine speed affect the overall efficiency of the turbocharger, which directly affects the performance, power output, and fuel economy of the engine.
In most, if not all, exhaust-driven turbocharger installations, a wastegate is employed to limit the maximum boost pressure developed by the turbocharger. Turbocharger speed regulation is achieved by diverting a portion of the exhaust gases through a wastegate instead of permitting all of the exhaust gases to pass through the turbine. Typically, the wastegate comprises a valve disposed in the exhaust flow path and an actuator for moving the valve. The actuator moves the valve between opened and closed positions in response to boost pressure. In the open position, the flow of the exhaust gases is diverted around the turbine housing whereas in the closed position, all of the exhaust gas travels through the turbine housing.
Prior art turbocharger systems are prone to certain failures. One of the principal sources of failure is overspeed of the turbine rotor assembly; that is, the turbine is rotated at revolutions per minute (RPM) higher than that for which the turbocharger is designed. Additionally, because the turbocharger is typically mounted near the exhaust manifold of the engine in order to efficiently receive exhaust gases for turning the turbine, the turbocharger is prone to overheating if its temperature is not regulated in some manner. If any of these conditions are left to exist for too long a period, the turbocharger will ultimately destroy itself
There is therefore a need for a system and method for controlling a turbocharger which allows the turbocharger to deliver the appropriate air mass flow to the engine to maximize engine performance and, at the same time, protects the turbocharger from excessive shaft speed and excessive turbine inlet temperature. The present invention is directed toward meeting these needs.